Machines such as, for example, dozers, loaders, excavators, motor graders, and other types of machines, are used in a variety of terrain-shaping operations. One such operation may be the removal and/or repositioning of material from a worksite. In such an operation, it may be desired to efficiently and precisely control the amount of material being moved at any instant by varying a cutting depth of a ground-engaging tool used to move the material. Manual control of the tool may be inefficient, particularly over a period of time as an operator tires. Additionally, manual control may be imprecise because an operator may react too slowly to changing terrain conditions. For example, as a contour of the terrain changes, quick tool adjustment may be necessary to account for changes in the machine pitch, the machine roll, and the terrain elevation that could cause an undesired removal and/or repositioning of the material. To achieve maximum control and efficiency, many machines rely on automatic systems to vary the cutting depth of the tool.
One method of automatically controlling the tool of an earthmoving machine is described in U.S. Pat. No. 6,845,311 (the '311 patent), issued to Stratton et al. on Jan. 18, 2002. The '311 patent discloses a system that controls the machine and a blade position of a bulldozer to maximize an efficiency of the machine in a load-carrying operation. The system of the '311 patent controls the machine and blade based on a measured slip coefficient, a machine speed, a machine slope, a machine pitch rate, a blade lift height, and a blade angle. The '311 system also adjusts the blade based on a position of the machine and a ground profile contained in a site map.
Although the system disclosed in the '311 patent may provide automated machine control, the control may be limited. Specifically, to adjust blade position, the '311 system relies on real-time measurements of both the pitch and the pitch rate of the machine and performing subsequent calculations based on those measurements. Then a corresponding blade adjustment can be made. While this sequence may be performed quickly enough to adjust the blade in a heavily loaded (i.e slow moving) machine, the sequence may be too slow to effectively control a machine with a light or empty load that moves quicker. This may be because a lightly loaded machine may have higher pitch and roll velocities that cause the machine to lurch more quickly than the control system processors and blade hydraulics of the '311 patent can respond. While the '311 patent may help alleviate some of the above problems, the '311 patent may not anticipate changing machine positions due to changing ground profiles or preemptively adjusting the position of the blade. Therefore under a light or empty load the '311 patent may react too slowly to prevent an undesired removal and/or repositioning of material.
The disclosed control system is directed to overcoming one or more of the problems set forth above.